This invention relates to electronic heat pumps and finned heat exchangers for transferring heat to and from such heat pumps.
For the sake of convenience, the invention will be described in relation to an electronic heat pump for a refrigeration system, but, it is to be understood that the invention is not limited thereto.
An electronic heat pump is defined herein as any heat pump or refrigerating module that directly depends upon flow of electrons and/or energy changes of electrons for its operation. This definition includes, but is not limited to, thermo-electric heat pumps and thermionic heat pumps.
The economic viability of a refrigeration system, which is based on the principles of a electronic heat pump, is primarily dependent on the efficiency of heat exchange between the electronic heat pump and two or more heat exchangers that collect and release the thermal load of refrigeration.
In a refrigeration system, heat can be dissipated effectively to the ambient air with the use of liquid coolants and radiators. However, the overall performance of a cooling system operating on an electronic heat pump is constrained by the heat transfer mechanism to the coolant fluid employed by the electronic heat pump.
In the prior art system disclosed in U.S. Pat. No. 5,715,684, effective heat transfer is achieved by directing jets of liquid onto the face of the thermoelectric module.
According to one aspect of the invention there is provided a heat exchanger for an electronic heat pump comprising:
a thermally conductive base plate having first and second surfaces;
the first surface being flat and adapted to make intimate surface contact with a surface of an electronic heat pump
the second surface being obverse to the first surface and supporting an array of thermally conductive fins, adjacent fins defining there between a plurality of channels.
In another prior art design, streams of coolant are forced to flow along a series of channels over the face of the electronic heat pumpxe2x80x94see U.S. Pat. Nos. 5,653,111 and 5,822,993.
Both of these designs offer limitations in terms of heat transfer capacity where the area available for heat dissipation to coolant is restricted to the face area of the electronic heat pump. In addition, fluid flow passages in Attey were made from non-conductive materials and no provision was made to incorporate additional heat flow paths to the coolant.
It is, therefore, an object of the present invention to extend the area of convective heat transfer between the electronic heat pump and coolant to a size significantly greater than the available area on the surface of the electronic heat pump.
According to another aspect of the invention there is provided a heat exchanger for one side of an electronic heat pump having a cold side and a hot side, said heat exchanger comprising:
(i) a heat exchanger having a thermally conductive base plate adapted to be thermally coupled by one face to one side of the electronic heat pump and having a plurality of spaced apart thermally conductive heat exchanger fins projecting outwardly from the other face, adjacent fins defining channels there between, and
(ii) a manifold having a recess for receiving the finned base plate and the backing plate, a fluid inlet to the recess and a fluid outlet from the recess.
According to another aspect of the invention there is provided an electronic heat pump and heat exchanger system comprising:
(i) an electronic heat pump having a hot side and a cold side,
(ii) a heat exchanger as defined above on at least one side of the electronic heat pump, and
(iii) means connecting the manifolds and adapted to provide a compressive sealing force between each base plate and the respective hot side and cold side of the electronic heat pump.
In one form of the invention, the thermally conductive base plate is integral with the fins.
The base plate of the heat exchanger may be joined to the face of the heat pump using soft solder with low melting point and good thermal conductivity such as Indium. Low melting point helps to carry out the process of fusing the base plate to the electronic heat pump with minimum thermal damage while, high thermal conductivity facilitates low thermal contact resistance at the joined interface.
A practical advantage of the invention is that, the geometrical arrangement of the heat exchanger enables the use of heat pump face area in its entirety in the heat dissipation process to the fluid. In previous designs, participating heat transfer surfaces of the electronic heat pump were obstructed by mechanical components such as seals, which lead to unsatisfactory operation of the peripheral parts of the electronic heat pump.
One aspect of the present invention relates to the application of a finned heat exchanger in a device which utilises an electronic heat pump to generate a thermal gradient. A microchannel between a pair of adjacent fins is defined as a channel whose width is approximately 0.1 to 5 mm and preferably about 0.4 mm. In a preferred embodiment, the fins which define the height of the microchannel are about 3.6 mm high and having a thickness of about 0.8 mm.